The senior engineering design projects at Calvin College tend to encourage ambitious thinking.

Among this year’s crop of senior projects is a concept that would take $4 million and 350 tons of steel to realize: It’s an automated, retractable pedestrian bridge designed to span the St. Joseph River channel in St. Joseph, Michigan.

The bridge, or at least a scale model of it, was produced by senior design team number 13, “The Pedestrians,” whose members are Craig Baker, 21, a mechanical engineer from Strathroy, Ontario; LeAnne Bock, 22, a civil and mechanical engineer from Almont, Michigan; Melanie Haagsma, 22, a civil engineer from Grand Rapids; and Abby Stemler, 21, a civil engineer from Elk River, Minnesota.

Their bridge had its genesis in an internship that saw Bock residing for a summer in St. Joe while she worked in nearby Bridgman. On the south side of the St. Joseph channel was Silver Beach, a popular summer destination, and on the north side was the aptly named North Pier Lighthouse, another popular summer destination. Bock found herself frequently giving directions to tourists who wanted to walk from one site to the other.

“It was a three-mile hike back up into town across a bridge that was also a highway,” she recounts. “So, they had to walk next to a semi-busy road and then back downtown through an industrial park and through a residential area to the other side.”

Bock remembered that long trek around the channel when the senior design team began meeting to brainstorm about a project.

“We were looking for a project that combined civil and mechanical aspects of engineering, and one of the ideas was a moveable bridge,” she says. “We said, ‘Why not?’”

The team put together a feasibility study that analyzed different bridge options -- a swing bridge, and lift bridge, among others -- before settling on a retractable bridge.

One bit of research was compelling, says Stemler.

“There were no retractable bridges in Michigan," she says. "The only ones were in New York City and Washington D.C.”

The team also consulted with Mike Tarazi, formerly of the Michigan Department of Transportation, and Dan Broekhuizen of URS.

“He was really knowledgeable about different aspects of moveable bridges,” Stemler says. “And he liked our idea, which was encouraging.”

The design the four settled on is a rack-and-pinion design powered by two motors.

“The motors transmit the power to the pinions, which will push the moving deck of the bridge open and closed,” says Baker, whose job it was to design the gearing system, shafts and bearings for the bridge.

The team divvied up all of the design chores for the project. Stemler analyzed the moving parts of the bridge as well as foundations and supports. Haagsma analyzed the stationary parts and handled a miscellany of chores related to the railings and lighting. Bock engineered rollers and alignment of mechanisms as well as designing a computer simulation of the working bridge.

Baker and Bock built the scale model of the bridge.

“They had the metal shop class. We didn’t,” Stemler says.

The quartet enjoyed working together.

“By the time we get to the end of our senior year, everybody in our department gets along really well because we work in close proximity,” Bock says.

There were challenges, however, one of which was coordinating between mechanical and civil disciplines.

“Civils usually design in the English system, and mechanicals design in the metric,” Stemler says. “So they had to adapt to us. We just told them that they had to do it in English because all of our codebooks are in English, and we’re not converting,” she adds, laughing.

The team won support for their proposed bridge, which would reduce the three-mile hike across the channel to a quarter-mile saunter, from John Hodgson, the assistant city manager of St. Joseph.

“He was really excited about the idea of having a bridge there,” says Haagsma. “We met with him a couple of times and toured the waterfront area.”

For now, because of the expense, the bridge will only be realized in the student model, which The Pedestrians showed off during the Senior Projects Open House, held 4:30 through 6 p.m. on Saturday, May 5 at the Calvin Engineering Building.

“Two hours of open house and 20 minutes of presentation,” Stemler sums up the event, which draws quite a crowd and includes a banquet for the graduating engineers. “We have a chance to show everyone why we’re hiding in the Engineering Building all year.”